1.NounA ship designed to break through ice so that it, or other ships coming behind, can navigate on frozen seas.
"The steel hulls of ice-breakers are much thicker than those of standard vessels."
2.NounA game, activity, humorous anecdote, etc., designed to ease tension and encourage interaction among individuals in a situation where they do not know each other well.
"The new college hallmates were awkward with each other at first, but after a game of charades as an icebreaker, they were laughing like old friends."
3.NounA lively song and dance routine at the start of a musical.